Finally got to make a 70 mph test run in the summer heat with the new fan clutch. The fan clutch helped, but the engine is still running far hotter than it should. This test was made without the AC running because the compressor seized up. I’ll retest the radiator cap and cooling system with my Stant pressure tester. All that can be left is a mildly blown head gasket. I have the diesel head gasket test kit too. Got some homework to do.

Here is a paper direct from Cummins. Although is applied to big rigs, it has great basic info on fuel economy. I personally have achieved a 10% mileage increase in my electric truck by adding synthetic lube to the trans, the diff and a zero toe front end alignment. Low rolling resistance tires make a great difference as well in my experience.

The belt was about 40% worn away. So a new one went in today.